I would place the HOB to the quarantine tank right away, with perhaps some cured liverock rubble as discussed in the other thread. If you don't have any live rock, then go ahead and use a new sponge, but yes you will need to do frequent water changes if you don't have enough or any active bacteria in the QT filter. . How much and often you do water changes will depend upon your water tests for ammonia and nitrite, you don't want either to get to high. But place your sponge in the sump so that 10-14 days later you can take out the live rock rubble and replace the rock with the sponge. At that time perhaps also place a new sponge in the sump so you will have one ready to go if need be in the future. Just don't forget to occasionally rinse it out in some water that you drain from the tank when doing periodic water changes, or else it could become a source of nitrates if allowed to get too dirty. Sorry if any of this is muddeled, I'm still at work and trying to get caught up before the weekend. Use this site for questions though, as people a good bit more experienced than myself always seem available for help and advice.